Method and composition for the sizing of paper using azetidinium and/or guanidine polymers

ABSTRACT

Compositions and methods are provided for the sizing of paper, to enhance the quality of images printed thereon. The novel sizing compositions contain as a sizing agent: (a) an azetidinium polymer, (b) a guanidine polymer, (c) a mixture of an azetidinium polymer and a guanidine polymer, or (d) a copolymer of an azetidinium monomer and a guanidine monomer. When applied to a paper substrate, such as in an internal or external sizing process, the sizing compositions result in a sized paper substrate that provides high quality printed images when printed with an ink containing a reactive dye having ionizable and/or nucleophilic groups capable of reacting with the sizing agent. Images printed on a paper substrate coated with the sizing compositions of the invention are bleed-resistant, water-resistant (e.g., water-fast), and/or are characterized by an enhanced chroma and hue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/282,595, filed Mar. 31, 1999, which is claims benefit of U.S.provisional patent application No. 60/082,697, filed Apr. 22, 1998, bothof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to the production of sizedpaper, and more particularly relates to a novel sizing process and novelcompositions useful in conjunction therewith.

BACKGROUND

As printing technology advances, paper manufacturers are faced with theincreasingly rigorous demands of their customers for high quality paperthat is economically attractive. For example, there is a keen demand forpapers that meet high quality standards with respect to brightness,opacity, and dry and/or wet strength, and that, upon printing with anyof a wide range of colorants, provide a water-resistant printed image.The customer further demands that such papers be amenable to use with avariety of printing techniques, including not only conventional printingtechniques, but also “impact free” printing techniques, e.g., inkjetprinting (particularly colored inkjet printing), laser printing,photocopying, etc.

In response, paper manufacturers have attempted to meet their customers'demands for such high quality paper through a process termed “sizing.”“Sizing,” which encompasses both “internal sizing” and “externalsizing,” affects the manner in which colorants and particularly inkinteract with the fibers of the paper. “Internal sizing” involvesintroduction of sizing compositions within the entire fibrous mass atthe pulp stage of paper manufacturing (i.e., to the wet pulp, or morespecifically, to the prepared papermaking furnish) before the stock isformed into a sheet, resulting in the distribution of the sizingcomposition within the entire fibrous mass that is subsequently used toproduce the flat fibrous paper sheet. “External sizing” (also termedsurface application, pasting, saturating or coating) involvesapplication of a sizing composition to at least one surface of a flatfibrous paper sheet, so that the sizing composition is present on or inat least one of the two faces of the flat fibrous sheet. Paper andpaper-based products are internally and/or externally sized to increasethe resulting paper's strength, resistance to picking and scuffing, andresistance to undue penetration of water, organic solvents, oils, inks,and various types of aqueous solutions. Sizing is also used to improvethe paper's smoothness and optical characteristics. In general, sizingis recognized to confer a number of advantages, including but notlimited to the foregoing, with perhaps resistance to penetration ofwater and aqueous inks (e.g., bleed resistance) of utmost importance.

Various materials have been used as external and/or internal sizingagents, such as conventional and modified starches, polyvinyl alcohol,cellulosic derivatives, gelatin, rosin, proteins such as casein, naturalgums and synthetic polymers. Internal sizing agents are generallyreferred to as acid, neutral, or alkaline internal sizes. Acid sizes aretypically rosin based and precipitated by alum. Neutral sizes may alsobe rosin-based, and are used at near-neutral pH, while alkaline sizesare synthetic materials such as alkenyl succinic anhydride (ASA) andalkyl ketene dimer (AKD). Although these materials are effective tovarious degrees under certain conditions, use of each is associated withcertain limitations. For example, it is often necessary to use largeamounts of these conventional sizing agents in order to provide paperhaving the desired properties. However, the opacity and brightness ofthe paper substrate decreases in direct proportion to the amount ofsizing agent applied to the paper. Moreover, as the amount of sizingagent and/or the cost of the sizing agent increases, the cost ofproducing the paper increases, making high quality papers having thedesired characteristics prohibitively expensive and not economicallyviable. Certain sizing agents impart relatively poor bleed resistanceand water resistance of imprinted inks, and thus must be used withinsolubilizing agents to ensure production of a paper havingsatisfactory water resistance.

Conventional and modified starches are the most common sizing agents inuse in the industry. Exemplary starch-based sizing agents includehydrophobic starches (see, e.g., U.S. Pat. No. 2,661,349), blends ofhydrophobic and non-hydrophobic starches (see, e.g., U.S. Pat. No.4,239,592; EP 350,668), and blends of treated starches and/or cationicstarches (see, e.g., U.S. Pat. No. 4,872,951; EP 620,315; U.S. Pat. No.5,647,898). However, while starches may provide improved porosity, thesecompounds generally do not provide for improved bleed resistance orwater resistance of inks printed on the treated paper substrates.

Several synthetic sizing agents are presently available, and may be usedin internal sizing and/or external sizing processes. Exemplary syntheticsizing agents include hydrophobic cellulose reactive sizing agents (see,e.g., U.S. Pat. Nos. 4,478,682; 3,840,486), cationic polymers (see,e.g., U.S. Pat. No. 3,006,806), and water-soluble, poly(aminoamide)resins (see, e.g., U.S. Pat. No. 4,478,682). Synthetic compounds havealso been used to enhance the dry and/or wet strength of paper (see,e.g., U.S. Pat. Nos. 5,138,669; 3,058,873; 5,510,004; 5,659,011), eitherat the internal sizing or external sizing steps. However, syntheticsizing agents tend to be expensive, due to both the cost of the startingmaterial and the amount that is required to provide a paper substratehaving the desired characteristics.

Unfortunately, the use of sizing agents normally results in a decreasein the porosity of the final paper substrate. Thus, while the finalsized paper substrate may have the desired brightness and opacity, itmay not provide for a printed image that is of a desired optical densityor color intensity. In addition, as the porosity of the paper increases,the paper becomes less amenable to various handling processes duringmanufacturing. For example, envelope manufacturers demand that the paperavailable to them have a relatively low porosity. If the porosity of thepaper is too high, the paper is too stiff for handling by the automaticindustrial devices for folding and sorting (e.g., devices of the“suction extractor” type) during envelope production. Moreover, incontrast to lower porosity papers, high porosity papers require slowermachine speeds and refining and draining operations that have relativelyhigh energy costs, both of which add up to decreases in plantproductivity, efficiency, and cost effectiveness.

There is a need in the field for sizing agents and methods that providean effective, cost efficient means for sizing paper, are amenable foruse with a wide variety of paper manufacture and post-manufacturehandling processes, and provide high quality, water-resistant images.

SUMMARY OF THE INVENTION

The present invention features novel sizing methods and sizingcompositions, wherein the sizing compositions are composed of a sizingagent selected from one of (a) an azetidinium polymer, (b) a guanidinepolymer, (c) a mixture of an azetidinium polymer and a guanidinepolymer, and (d) a copolymer of an azetidinium monomer and a guanidinemonomer. When applied to a paper substrate, such as in an externalsizing process, the sizing compositions provide a coated paper substratethat yields high quality printed images when printed with an inkcontaining a reactive dye having ionizable and/or nucleophilic groupscapable of reacting with the sizing agent. Images printed on a papersubstrate coated with the sizing composition of the invention arebleed-resistant, water-resistant (e.g., water-fast), and/or arecharacterized by an enhanced chroma and hue.

It is a primary object of the invention to address the above-mentionedneed in the art by providing a sizing composition that efficiently bindscolorant upon printing, and thus provides an economical, efficient meansfor processing of paper that provides a high quality printed image.

Another object of the invention is to provide a printed, sized papersubstrate that is of high quality, bleed-resistant, and provideswater-resistant (e.g., water-fast) images that are of a highly desirableoptical density and brightness.

Still another object of the invention is to provide a method for sizingpaper using the sizing compositions of the invention.

Still an additional object of the invention is to provide a method forprinting on a sized paper substrate to provide water-resistant (e.g.,water-fast) images thereon.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions and Nomenclature

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a sizing agent” in a composition means that more than onesizing agent can be present in the composition, reference to “apolymer,” as in “a guanidine polymer” or “an azetidinium polymer”includes more than one such polymer, and the like.

The term “paper” or “paper substrate” is meant to encompass a substratebased on cellulosic fibers; synthetic fibers such as polyamides,polyesters, polyethylene, and polyacrylic fibers; inorganic fibers suchas asbestos, ceramic, and glass fibers; and any combination ofcellulosic, synthetic, and inorganic fibers. The paper substrate may beof any dimension (e.g., size or thickness) or form (e.g., pulp, wetpaper, dry paper, etc.). In most instances, the “paper” or “papersubstrate” has not been subjected to an external sizing process prior totreatment according to the methods of the invention. Where the papersubstrate is used in external sizing, the paper substrate is preferablyin the form of a flat or sheet structure, which structure may be ofvariable dimensions (e.g., size and thickness). “Paper,” particularly asused in the context external sizing, is thus meant to encompass printingpaper (e.g., inkjet printing paper, etc.), writing paper, drawing paper,and the like, as well as board materials such as cardboard, posterboard, Bristol board, and the like.

The term “sheet” or “flat structure” is not meant to be limiting as todimension, roughness, or configuration of the substrate useful with thepresent invention, but rather is meant to refer to a product suitablefor external sizing.

“Sized paper substrate” is a paper substrate as described above that hasapplied to its surface and/or is saturated with one or more of thesizing compositions of the present invention. The sizing composition ofthe invention is preferably applied in an external sizing step, but mayalso be applied as a pretreatment (e.g., prior to printing),simultaneously with printing, or as an after-treatment. The sizingcompositions of the invention are applied in quantities suitable toaccomplish external sizing and to provide desired characteristics, suchas bleed resistance, water resistance (e.g., water-fastness) of an inkprinted on sized paper substrate, etc. Typical amounts of sizingcomposition applied generally range from about ten to about five hundredpounds per ton of paper substrate, preferably from about thirty to aboutfive hundred pounds per ton of paper substrate.

“Aqueous based ink” refers to an ink composed of an aqueous carriermedium and a colorant, such as a dye or a pigment dispersion. An aqueouscarrier medium is composed of water or a mixture of water and one ormore water-soluble organic solvents. Exemplary aqueous based inkcompositions are described in detail below.

“Colorant” as used herein is meant to encompass dyes, pigments, stains,and the like compatible for use with the polymer coatings of theinvention.

The term “colorant-reactive component” as used herein refers to acomponent (e.g., a chemical moiety) of a sizing agent that is capable ofreacting with a selected colorant, particularly a colorant having anucleophilic and/or ionizable group, to form a sizing agent-colorantcomplex. The sizing agent-colorant complex is formed through either acovalent, electrostatic, or ionic association between thecolorant-reactive component of the sizing agent and the colorant. When asizing agent having a colorant-reactive component and a selectedcolorant from a sizing agent-colorant complex in the context of aprinted image on a sized paper substrate, the association between thecolorant and the color-reactive component of the sizing agent iseffective to impart advantageous qualities to the printed image on thesized paper substrate, particularly with respect to water resistance,enhanced optical density, enhanced brightness, and the like.

The term “organic solvent” is used herein in its conventional sense torefer to a liquid organic compound, typically a monomeric organicmaterial in the form of a liquid, preferably a relatively nonviscousliquid, the molecular structure of which contains hydrogen atoms, carbonatoms, and optionally other atoms as well, and which is capable ofdissolving solids, gases or liquids.

The term “significant” as when used with reference to “significantlyenhanced brightness” or “significantly improved water-fastness”generally refers to a difference in a quantifiable, measurable, orotherwise detectable parameter, e.g., optical density, LAB graphs (colorsphere), dot spread, bleed through, between the two groups beingcompared (e.g., unsized versus sized paper substrates) that isstatistically significant using standard statistical tests. For example,the degree of visual wicking or water-fastness in a sized papersubstrate as detected in a print assay may be quantified using standardmethods, and the degree of wicking or water-fastness under differentconditions can be compared for both sized and unsized paper substratesto detect statistically significant differences.

The term “fluid resistance” is used herein to describe the resistance ofa paper substrate to penetration by a fluid, with the term “waterresistance” specifically referring to resistance of a paper substrate topenetration by a fluid.

The term “water-fast,” is used herein to describe a form of waterresistance, and which is normally used to refer to the nature of the inkcomposition after drying on a substrate. In general, “water-fast” meansthat the dried composition is substantially insoluble in water, suchthat upon contact with water, the dried ink retains at least about 70%,preferably at least about 85%, and more preferably at least about 95%,of optical density.

The term “bleed resistance” is meant to refer to the retardation of thepenetration of water into paper, which retardation is associated withcreation of a low energy hydrophobic surface at the fiber-waterinterface which increases the contact angle formed between a drop ofliquid and the surface, and thus decreases the wettability. Contactangles have been shown to be sensitive to molecular packing, surfacemorphology, and chemical constitution of the paper substrate and anycomponents added thereto.

The term “rub resistance” is normally meant to refer to a characteristicof the ink composition after drying on a substrate, more specifically,the ability of a printed image to remain associated with the substrateupon which it is printed despite application of force (e.g., rubbing) tothe printed image. In general, “rub resistant” means that the dried inkcomposition is substantially resistant to rubbing force so that thedried ink retains at least about 70%, preferably at least about 85%, andmore preferably at least about 95%, of optical density after rubbing ofthe printed image.

The term “alkyl” as used herein refers to a branched or unbranchedsaturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl,tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, as well ascycloalkyl groups such as cyclopentyl, cyclohexyl and the like. The term“lower alkyl” intends an alkyl group of 1 to 6 carbon atoms, preferably1 to 4 carbon atoms.

The term “alkylene” as used herein refers to a difunctional, branched orunbranched saturated hydrocarbon group of 1 to 24 carbon atoms,including without limitation methylene, ethylene, ethane-1,1-diyl,propane-2,2-diyl, propane-1,3-diyl, butane-1,3-diyl, and the like.“Lower alkylene” refers to an alkylene group of 1 to 6 carbon atoms.

The term “alkoxy” as used herein intends an alkyl group bound through asingle, terminal ether linkage; that is, an “alkoxy” group may bedefined as —OR where R is alkyl as defined above. A “lower alkoxy” groupintends an alkoxy group containing 1 to 6 carbon atoms.

“Halo” or “halogen” refers to fluoro, chloro, bromo or iodo, and usuallyrelates to halo substitution for a hydrogen atom in an organic compound.

The term “polymer” is used herein in its conventional sense to refer toa compound having two or more monomer units, and is intended to includehomopolymers as well as copolymers. The term “monomer” is used herein torefer to compounds that are not polymeric.

“Optionally” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances where itdoes not. For example, the phrase “optionally substituted” aromatic ringmeans that the aromatic ring may or may not be substituted and that thedescription includes both an unsubstituted aromatic ring and an aromaticring bearing one or more substituents.

Overview of the Invention

The present invention is based upon the discovery that a compositionhaving a sizing agent that is one of (a) an azetidinium polymer, (b) aguanidine polymer, (c) a mixture of an azetidinium polymer and aguanidine polymer, or (d) a copolymer of an azetidinium monomer and aguanidine monomer, is highly effective as a sizing composition. Paperthat has been treated with a sizing composition of the inventionultimately provides high quality printed images having improved colorfastness (printed images which do not run when exposed to moisture) andexhibits substantially non-reversible binding of aqueous colorants.These images are therefore characterized as “water-resistant” or“water-fast” due to the characteristics of the printed image followingexposure to water.

The sized paper substrates of the invention can be used in conventionalprinting, or with digital printing (particularly inkjet printing,including drop-on-demand and continuous printing) to provide highlybrilliant, printed images that are significantly improved in colorquality, for example, with respect to chroma and hue, when compared tounsized paper substrates and/or to paper substrates sized withconventional sizing compositions. The sizing compositions and theirmethods of use according to the present invention thus provide a numberof advantages over conventional sizing methods and sizing compositions.

The sizing compositions, methods of sizing using the sizing compositionsdescribed herein, and other features of the invention are described ingreater detail below.

Sizing Compositions

The sizing compositions of the invention are composed of a sizing agentselected from the group consisting of (a) an azetidinium polymer, (b) aguanidine polymer, (c) a mixture of an azetidinium polymer and aguanidine polymer, and (d) a copolymer of an azetidinium monomer and aguanidine monomer. In general, the sizing agents have acolorant-reactive component, which is capable of reacting with aselected colorant, particularly a colorant having a nucleophilic and/orionizable group, to form a sizing agent-colorant complex through acovalent, electrostatic, or ionic association. The association of thesizing agent and colorant imparts bleed resistance, water resistance(e.g., water-fastness), and other desirable characteristics to theprinted sized paper substrate. In addition to the sizing agent, thesizing compositions can include components such as binders, pigments,and other additives.

The present sizing compositions can be readily prepared fromcommercially available starting materials and/or reagents, arecompatible with additional binders or additives, can be used with avariety of base papers, and are compatible with a variety of printingmethods, including conventional and digital printing methods(particularly inkjet printing, including drop-on-demand printing andcontinuous printing), and can also be used with existing commercialpaper production processes and equipment. The sizing composition isinexpensive to prepare, and due to their efficacy, generally less sizingagent is needed to provide a sized paper substrate having theadvantageous features described herein. The sizing compositions of theinvention are also easy to handle due to their solubility in water(i.e., the sizing agents are hydrophilic polymers), and do not requirethe use of large volumes of organic solvents. The novel sizingcompositions herein also possess good film-forming properties.

The sized paper substrate prepared using the composition of theinvention exhibits improved durability, as evidenced by improved paperstrength (e.g., tear strength), and stability upon prolonged storage.The sized paper does not discolor or yellow, and maintains a high degreeof brightness for extended periods of time. Paper substrates treatedwith the sizing compositions of the invention react rapidly andsubstantially irreversibly with a number of aqueous based colorants,thus providing a versatile sizing system for use with a wide variety ofavailable colorants. Furthermore, because the colorant reacts quicklywith the sizing compositions, the sized printed substrate does notrequire a separate curing step, but rather is fast-drying. Thisfast-drying characteristic provides for printed images that are“non-sticky,” thus allowing the printed sized paper substrate to behandled immediately after printing, for example, to allowing stacking.The sized paper substrate of the invention can also be used to prepareimages with varying degrees of gloss, depending upon variations inpigment.

In addition to their water resistance, paper substrates sized with asizing composition of the invention are highly bleed-resistant (asevidenced by small dot size measurements, i.e., less wicking action) andrub-resistant.

The various components of the sizing compositions will now be described.

Sizing Agents

Sizing agents in the sizing compositions of the invention generallycomprise an azetidinium polymer, a guanidine polymer, a copolymer of anazetidinium monomer and a guanidine monomer, or a mixture of anazetidinium polymer and a guanidine polymer. In general, the sizingagent represents approximately 5 wt. % to 95 wt. % of the sizingcomposition, typically 10 wt. % to 95 wt. % of the sizing composition,based upon total solids weight of the composition after drying.

Azetidinium Polymers

In one embodiment, the sizing agent is an azetidinium polymer. An“azetidinium polymer” is a polymer comprised of monomeric subunitscontaining a substituted or unsubstituted azetedine ring (i.e., a fourmembered nitrogen-containing heterocycle). In general, the azetidiniumpolymers useful herein are composed of monomer units having thestructural formula (I):

in which R¹ and R² are independently lower alkylene, X⁻ is an anionic,organic or inorganic counterion, and Y¹, Y² and Y³ are selected from thegroup consisting of hydrogen, hydroxyl, halo, alkoxy, alkyl, amino,carboxy, acetoxy, cyano and sulthydryl. Preferred such polymers arewherein R¹ and R² are methylene, X⁻ is selected from the groupconsisting of halide, acetate, methane sulfonate, succinate, citrate,malonate, fumarate, oxalate and hydrogen sulfate, Y¹ and Y³ areindependently hydrogen or lower alkyl, and Y² is hydrogen or hydroxyl.In particularly preferred azetidinium polymers herein, Y¹ and Y³ arehydrogen and Y² is hydroxyl.

The azetidinium polymer may be a homopolymer, or it may be a copolymer,wherein one or more non-azetidinium monomer units are incorporated intothe polymer structure. Any number of comonomers may be employed to formsuitable azetidinium copolymers for use herein; however, a particularlypreferred azetidinium copolymer is aminoamide azetidinium. Further, theazetidinium polymer may be essentially straight-chain or it may bebranched or crosslinked.

Azetidinium polymers can associate with colorant in two different ways.First, the azetidinium polymer can associate with colorant through anionic interaction, where the colorant provides anionic groups, such ascarboxy or sulfonate, that can ion-exchange with the polymer counterions(X⁻ in Formula (I), above), thus fixing the colorant to the sized paper.substrate via an electrostatic-type interaction. Second, nucleophilicgroups present within the colorant can react with the azetidinium groupsof the polymer via a ring-opening reaction. A characteristicring-opening reaction of an azetidinium polymer of the invention may beillustrated as follows:

The colorant (“−Nuc−) thus covalently bonds to the polymer coating, toform a cross-linked polymer-colorant complex. Colorant thus applied to asized substrate is rapidly and irreversibly bound to the papersubstrate.

The percentage of reactive azetidinium groups in the polymer can beadjusted in a controlled manner to tailor the number of reactive groupsin the polymer. Azetidinium groups are insensitive to pH change;however, such groups are highly sensitive to the presence of anionic andnucleophilic species. In some cases, it may be desirable to adjust thereaction conditions used to prepare the azetidinium polymer (e.g., byraising the pH) to generate anionic groups within the polymer, whichthen participate in intramolecular crosslinking.

A preferred azetidinium polymer for use in the present invention isshown in Formula (II)

Commercially available such polymers include “AMRES®,” available fromGeorgia Pacific Resins, Inc., Atlanta, Ga., “KYMENE®,” from Hercules,Inc., Wilmington, Del., and “Polycup®,” also from Hercules, Inc. Theseazetidinium polymers are generally referred to aspoly(aminoamide)-epichlorohydrin (PAE) resins; such resins are typicallyprepared by alkylating a water-soluble polyamide containing secondaryamino groups with epichlorohydrin. Other suitable azetidinium polymerswill be known to those skilled in the art and/or are described in thepertinent texts, patent documents, and literature references; see, forexample, Moyer, et al., in Wet Strength in Paper and PaperBoard, TappiMonograph Series No. 29, Tappi Press, Ch. 3, p. 33-37 (1965); Chan, inTappi Wet and Dry Strength Short Course, Tappi Press, Atlanta, Apr.13-15, 1988; and Espy, in Wet Strength Resins and Their Application,Ed., Lock L. Chan, Tappi Press, Atlanta, Ga. (1994).

(B) Guanidine Polymers

In another embodiment, the sizing agent is a guanidine polymer, alsotermed a “polyguanidine.”. The guanidino group is extremely basic,possessing a pKa of about 12-13. Polyguanidine polymers for use in theinvention are typically provided as acid salts wherein the iminenitrogen atoms are for the most part in protonated form.

In general, guanidine polymers useful as sizing agents in the presentinvention are either homopolymers or copolymers. All guanidine polymersherein are comprised of recurring monomer units having the structuralformula

wherein R³ is hydrogen or lower alkyl and R⁴ is hydrogen, alkyl, alkoxy,or hydroxyl-substituted alkoxy. Preferably, R³ and R⁴ are hydrogen.Particularly preferred guanidine polymers for use herein are comprisedof monomer units having the structural formula (IV)

wherein n is an integer in the range of 1 to 10 inclusive, R³ ishydrogen or lower alkyl and R⁴ is hydrogen, alkyl, alkoxy, orhydroxyl-substituted alkoxy. Preferably, R³ and R⁴ are hydrogen.

A particularly preferred guanidine polymer for use in the methods andcompositions of the invention has the structure of formula (IV) whereinR³ and R⁴ are H and n is 6(3,12-diimino-2,4,11,13-tetraazatetradecanediimidamide), available underthe tradenames “BAQUACIL®” and “VANTOCIL®,” from Zeneca, Inc.

Polyguanidine polymers of the invention react electrostatically withanionic groups present in the dye via ion-exchange type interactions, torapidly and irreversibly bind anionic type dyes to print substratescoated with such polymers.

(C) Mixtures of Azetidinium Polymers and Guanidine Polymers

In another embodiment, the sizing agent comprises a mixture of anazetidinium polymer and a guanidine polymer. The two polymers may bepresent in any suitable ratio relative to one another. The relativeamounts of polyguanidine and polyazetidinium can range from about 0.05%polyguanidine/99.95% polyazetidinium to 0.05% polyazetidinium/99.95%polyguanidine. The actual relative amounts of polyguanidine andpolyazetidinium will vary according to the composition of the ink to beused (e.g., the nature of the colorant in the ink), the nature of thepaper substrate, and other factors affecting the use of the polymers,such as the relative market price for each polymer. In general, it ispreferable to use a smaller amount of guanidine relative to azetidinium.

In this embodiment, it is important that the pH of the sizingcomposition be acidic, as the composition tends to gel at basic pH. Ifnecessary, then, an acid should be added to the sizing composition toensure that the pH is below 7.0, preferably less than about 5.5, andmost preferably in the range of about 1.0 to 5.5. Suitable acids includesulfuric acid, hydrochloric acid, acetic acid, and the like.

Although it will be appreciated that any of a number of azetidinium orguanidine polymers can be used to prepare the sized substrates andsizing compositions described herein, a preferred polymer is a poly(aminoamide)-azetidinium polymer, e.g., a polyazetidinium chloride-basedpolymer, such as a polyamide-polyamine-epichlorohydrin resin.

(D) Copolymers of Azetidinium Monomers and Guanidine Monomers

In another embodiment, the sizing agent is a copolymer of an azetidiniummonomer unit and a guanidine monomer unit. In general, the azetidiniummonomer unit has the structural formula (I)

in which R¹ and R² are independently lower alkylene, X⁻ is an anionic,organic or inorganic counterion, and Y¹, Y² and Y³ are selected from thegroup consisting of hydrogen, hydroxyl, halo, alkoxy, alkyl, amino,carboxy, acetoxy, cyano and sulfhydryl. Preferred monomers are whereinR¹ and R² are methylene, X³¹ is selected from the group consisting ofhalide, acetate, methane sulfonate, succinate, citrate, malonate,fumarate, oxalate and hydrogen sulfate, Y¹ and Y³ are independentlyhydrogen or lower alkyl, and Y² is hydrogen or hydroxyl. In particularlypreferred azetidinium monomers, Y¹ and Y³ are hydrogen and Y² ishydroxyl. The guanidine monomer has the structural formula (III)

or the structural formula (IV)

wherein R³, R⁴ and n are as defined earlier herein.

The ratio of azetidinium monomers to guanidine monomers in thecopolymer, as well as the distribution of each monomer type in thecopolymer, can be varied according to a number of factors, and may be,for example, tailored for use with specific colorants having certaintypes of ionic and/or nucleophilic groups. The precise composition ofthe copolymer may also be varied to best accommodate the nature of thepaper substrate to be sized.

Film-forming Binders

The sizing compositions of the invention preferably include afilm-forming binder. By “film-forming binder” is meant a substance thatprovides for improved strength of a paper substrate upon application ofthe substance to the substrate. “Film-forming binders” used inconnection with the sizing compositions of the invention include anyfilm-forming binder that is compatible with the sizing agent of thecomposition. Exemplary film-forming binders include, but are notnecessarily limited to: polysaccharides and derivatives thereof, e.g.,starches, cellulosic polymers, dextran and the like; polypeptides (e.g.,collagen and gelatin); and synthetic polymers, particularly syntheticvinyl polymers such as poly(vinyl alcohol), poly(vinyl phosphate),poly(vinyl pyrrolidone), vinyl-pyrrolidone-vinyl acetate copolymers,vinyl alcohol-vinyl acetate copolymers, vinyl pyrrolidone-styrenecopolymers, and poly(vinylamine), and cationic film-forming binders suchas quaternized vinyl pyrrolidone-dimethylaminoethyl-methacrylatecopolymer, dimethylaminoethyl-methacrylate-co-methyl methacrylate,polydiallyldimethyl ammonium chloride and quaternized aminoacrylatepolymers. The sizing agents herein are themselves film-formingsubstances; however, it is generally desirable to use these sizing agentcompositions with additional film-forming substances.

Polysaccharide binders: Starches, as noted above, represent one categoryof suitable film-forming binders for use herein. Suitable starches maybe any of a variety of natural, converted, and synthetically modifiedstarches. Exemplary starches include, but are not necessarily limited tostarch (e.g., SLS-280 (St. Lawrence Starch)), cationic starches (e.g.,Cato-72 (National Starch), hydroxyalkylstarch, wherein the alkyl has atleast one carbon atom and wherein the number of carbon atoms is suchthat the material is water soluble, preferably from about 1 to about 10carbon atoms, such as methyl, ethyl, propyl, butyl, or the like (e.g.,hydroxypropyl starch #02382 (PolySciences, Inc.), hydroxyethyl starch#06733 (PolySciences, Inc.), Penford Gum 270 and 280 (Penford), andFilm-Kote (National Starch)), starch blends (see, e.g., U.S. Pat. No.4,872,951, describing a blend of cationic starch and starch treated withan alkyl or alkenyl succinic anhydride (ASA), preferably 1-octenylsuccinic anhydride (OSA)), and the like. The film-forming binder canalso be a synthetically produced polysaccharide, such as a cationicpolysaccharide esterified by a dicarboxylic acid anhydride (see, e.g.,U.S. Pat. No. 5,647,898). Additional saccharide binders includecellulosic materials such as alkyl celluloses, aryl celluloses, hydroxyalkyl celluloses, alkyl hydroxy alkyl celluloses, hydroxy alkylcelluloses, dihydroxyalkyl cellulose, dihydroxyalkyl cellulose, hydroxyalkyl hydroxy alkyl cellulose, halodeoxycellulose, amino deoxycellulose,dialkylammonium halide hydroxy alkyl cellulose, hydroxyalkyl trialkylammonium halide hydroxyalkyl cellulose, dialkyl amino alkyl cellulose,carboxy alkyl cellulose salts, cellulose sulfate salts,carboxyalkylhydroxyalkyl cellulose and the like). Still additionalfilm-forming binders of this type include dextran (e.g., dialkylaminoalkyl dextran, amino dextran, and the like), carrageenan, Karayagum, xanthan, guar and guar derivatives, (e.g., carboxyalkylhydroxyalkyl guar, cationic guar, and the like), and gelatin.

Additional exemplary film-forming binders for use in the sizingcompositions of the invention include resins (e.g., such as formaldehyderesins such as melamine-formaldehyde resin, urea-formaldehyde resin,alkylated urea-formaldehyde resin, and the like ), acrylamide-containingpolymers (e.g., poly(acrylamide), copolymers,poly(N,N-dimethylacrylamide), and the like),poly(alkyleneimine)-containing polymers (e.g., poly(ethyleneimine),poly(ethyleneimine) epichlorohydrin, alkoxylated poly(ethylene imine),and the like), polyoxyalkylene polymers (e.g., poly(oxymethylene),poly(oxyethylene), ethylene oxide/propylene oxide copolymers, ethyleneoxide/2-hydroxyethyl methacrylate/ethylene oxide and ethyleneoxide/hydroxypropyl methacrylate/ethyleneoxide triblock copolymers,ethylene oxide-4-vinyl pyridine/ethylene oxide triblock copolymers,ethylene oxide-isoprene/ethylene oxide triblock copolymers,epichlorohydrin-ethylene oxide copolymer, and the like), etc.

Any suitable mixtures of the above exemplary film-forming binders can beused in any effective relative amounts, although typically thefilm-forming binder, if present, represents approximately 1 wt. % to 40wt. %, preferably 1 wt. % to 25 wt. %, most preferably 1 wt. % to 15 wt.% of the composition, after drying on a substrate. Starches and latexesare of particular interest because of their availability andapplicability to paper.

Other Sizing Composition Components

Additional sizing composition components may include, but are notnecessarily limited to, inorganic fillers, anti-curl agents, oradditional conventional components such as a surfactant, plasticizer,humectant, UV absorber, light fastness enhancer, polymeric dispersant,dye mordant, optical brightener, or leveling agent, as are commonlyknown in the art. Illustrative examples of such additives are providedin U.S. Pat. Nos. 5,279,885 and 5,537,137. The sizing compositions mayadditionally contain a colorant (e.g., a pigment, dye (e.g., ionizabledye, nucleophilic dye, etc.), or other colorant) to provide forwhiteness or color of the sized paper substrate. The sizing compositionsmay also further include a crosslinking agent, such as zirconiumacetate, ammonium zirconium carbonate, or the like, for intramolecularand/or intermolecular crosslinking of sizing agent(s) in the sizingcomposition and/or a chelating agent such as boric acid. Additionalcomponents that may be desirable for use in the sizing compositions ofthe invention, as well as guidance for the use of such components and ageneral description of paper chemistry, are found in Paper Chemistry,2^(nd) Edition, Roberts, ed., Blackie Academic & Professional, Glasgow,UK (1994).

The sizing composition will generally be provided in an aqueous liquidvehicle, although small amounts of a water-soluble organic solvent maybe present. The aqueous liquid vehicle will generally be water, althoughother nonorganic compounds that are either water soluble or watermiscible may be included as well. It may on occasion be necessary to adda solubilizing compound during preparation of the sizing composition sothat the components dissolve in the aqueous liquid vehicle, e.g., aninorganic base such as ammonia and/or an organic amine. Suitable organicamines include lower alkyl-substituted amines such as methylamine,dimethylamine, ethylamine, and trimethylamine, as well as ethanolamine,diethanolamine, triethanolamine, and substituted ethanolamines,typically lower alkyl-substituted ethanolamines such as N-methyl andN,N-dimethyl ethanolamines, and morpholine. Such compounds are alsouseful for bringing the pH into the desired range for basicformulations, and, if present, will generally represent not more thanabout 20 wt. % of the composition, and in most cases will represent notmore than about 10 wt. % of the composition.

Application of Sizing Compositions to Paper Substrates

The sizing compositions of the invention can be applied to a substrate,e.g., a paper substrate, by any of a number of conventional processescommonly employed in the art. Generally, the sizing compositions of theinvention are applied by means of a rod, roll, flexopress, blade, orair-knife coater in amounts ranging from about 10 to 500, preferably 30to 500, pounds per ton of substrate. For external sizing, the sizingcomposition is applied to a paper substrate to achieve a desired sizingcomposition layer thickness selected according to the particularapplication. Application of a coating in a selected thickness canreadily be done by one of skill in the art using known techniques, forexample, by varying the sizing agent concentration and number ofcoatings and through selection of the application means.

The sizing composition as described above is applied to any desirablepaper substrate, usually to a type of paper substrate commonly used inprinting. Substrates for use in the invention include cellulose andnon-cellulose type substrates (e.g., synthetic fibers such aspolyamides, including nylon, polyesters, polyethylene, and polyacrylicfibers; protein-based fibers such as silk; inorganic fibers such asasbestos, ceramic, and glass fibers), and/or any combination ofcellulosic, synthetic, and inorganic fibers, with porous cellulosesubstrates being preferred. Preferred substrate for use herein isgenerally free cut sheet paper, with exemplary paper substratesincluding, but not limited to, copier grade paper, business card stock,resin-coated papers, cartons such as milk cartons and cardboard giftboxes. Additional exemplary substrates for use in the invention includepolyester films such as “MYLAR” flexible film, polysulfones, cellulosetriacetates, and the like. Coated transparent films are alsocontemplated.

Sizing Processes

In general, sizing encompasses both internal and external sizing.“Internal sizing” generally involves introduction of sizing compositionsat the pulps stage of paper manufacturing, resulting in the distributionof the sizing composition within the fibrous mass subsequently used toproduce a flat fibrous structure, e.g., a sheet of paper. “Externalsizing,” also called surface application, pasting, saturating, orcoating, involves application of a sizing composition to at least onesurface of a flat fibrous paper structure, so that the sizingcomposition is present on or in at least one of t he two faces of theflat fibrous paper. External sizing also saturates the paper to variousextents depending on the degree of internal sizing.

Internal sizing processes are well known in the art. Generally, in ternal sizing is accomplished by adding the sizing agent to the pulp,preferably with continuous mixing at the dosing point. In general, theexternal sizing process of the invention involves application of asizing composition of the invention to a surface of a paper substrate.Any suitable technique can be used for application of the sizingcompositions of the invention as an internal or external sizing agentfor a paper substrate. Exemplary external sizing techniques include, butare not necessarily limited, to, size press treatment, dip coating,reverse roll coating, extrusion coating, and the like. For example, thesizing composition can be applied with a size press by dip coating andcan be applied by solvent extrusion. The size press can be a sheet-fedsize press or a size press employing a continuous web, preferably acontinuous web size press.

The invention also features a paper substrate that has been sized usingthe sizing compositions and methods of the invention as described above.As noted in the preceding section, the sized paper substrate may becellulosic or non-cellulosic, and may comprise any combination ofcellulosic, synthetic and inorganic fibers. The sized paper substratemay be of any size and is preferably in the form of a flat or sheetstructure, which may be of variable dimensions. Of particular interestin the present invention are sized paper substrates that are suitablefor use in as inkjet printing paper, writing paper, drawing paper, andthe like.

Method for Providing Water-resistant Images on Paper

The invention also features a method for providing a water-resistant(e.g., water-fast) image on paper by first applying to the surface of apaper substrate a sizing composition of the invention to the surface ofa paper substrate to produce a sized substrate, and then applying acolorant to the sized substrate, where the colorant contains reactiveionizable and/or nucleophilic groups capable of reacting with the sizingagent.

In general, aqueous inks are used in the preparation of a printed imageon the sized paper substrates of the invention. The aqueous ink may beany suitable ink having a colorant, e.g., a pigment, dye, or stain,having one or more reactive groups suitable for reacting, eithercovalently or ionically, with a colorant-reactive component of a sizingagent of the sizing composition present on the sized paper substrate.The selection of the specific ink and the colorant of the ink can varywith colorant-reactive component of the sizing agent used in the sizingcomposition. For example, where the colorant-reactive component is anazetidinium group, the colorant has a nucleophilic group for reactionwith the azetidinium group. Thus, preferred colorants for use inprinting on a sized paper substrate having a polyazetidinium polymer inthe polymer coating are those containing one or more nucleophiles, e.g.,having an amino, carboxy, sulfonato, thiosulfonato, cyano, hydroxy orsulfido group or the like. Preferred colorants for use in printing asized paper substrate having a polyguanidine polymer in the polymercoating are those containing an anionic group, e.g., having a carboxy,sulfonato, thiosulfonato, cyano, halo, or phosphonato group or the like.

Preferably, the inks used in conjunction with the sized paper substrateof the invention are inkjet inks. Water-soluble colorants for use in theinvention may be acid dyes, direct dyes, basic dyes or dispersive dyes,and preferred dyes for use in the invention are described in U.S. Pat.Nos. 5,425,805, 5,537,137, and 5,441,561.

The selection of the aqueous based ink will depend upon the requirementsof the specific application, such as desired surface tension, viscosity,drying time, the type of paper substrate upon which the ink is to beapplied (printing medium), and the like. The aqueous liquid vehicle ofinks suitable for use in the invention will generally be deionizedwater, although other nonorganic compounds which are either watersoluble or water miscible may be included as well. The colorant may bedissolved, dispersed or suspended in the aqueous liquid vehicle, and ispresent in an amount effective to provide the dried ink with the desiredcolor and color intensity.

In some instances, the dye is contained in a carrier medium composed ofink and a water soluble organic solvent. For applications utilizing sucha carrier medium, representative solvents include polyols such aspolyethylene alcohol, diethylene glycol, propylene glycol, and the like.Additional solvents are simple alcohols such as ethanol, isopropanol andbenzyl alcohol, and glycol ethers, e.g., ethylene glycol monomethylether, diethylene glycol monoethyl ether. Representative examples ofwater soluble organic solvents are described in U.S. Pat. No. 5,085,698and U.S. Pat. No. 5,441,561.

Preferred colorants contained in the inks useful with the invention aredyes, including azo or “direct” dyes as well as dyes containing acidicgroups (e.g., carboxylate, phosphonate or sulfonate moieties), basicgroups (e.g., unsubstituted amines or amines substituted with 1 or 2alkyl, typically lower alkyl, groups), or both. Specific examples ofsuitable colorants include, but are not limited to, the following:Dispersol Blue Grains (Zeneca, Inc.), Duasyn Acid Blue (HoechstCelanese), Duasyn Direct Turquoise Blue (Hoechst Celanese),Phthalocyanine blue (C.I. 74160), Diane blue (C.I. 21180), Pro-jet Cyan1 (Zeneca, Inc.), Pro-jet Fast Cyan 2 (Zeneca, Inc.), Milori blue (aninorganic pigment equivalent to ultramarine) as cyan colorants;Dispersol Red D-B Grains (Zeneca, Inc.), Brilliant carmine 6B (C.I.15850), Pro-jet magenta 1 (Zeneca, Inc.), Pro-jet Fast magenta 2(Zeneca, Inc.), Brilliant Red F3B-SF (Hoechst Celanese), Red 3B-SF(Hoechst Celanese), Acid Rhodamine (Hoechst Celanese), Quinacridonemagenta (C.I. Pigment Red 122) and Thioindigo magenta (C.I. 73310) asmagenta colorants; Dispersol Yellow D-7G 200 Grains (Zeneca, Inc.),Brilliant yellow (Hoechst Celanese), Pro-jet yellow 1 (Zeneca, Inc.),Pro-jet Fast Yellow 2 (Zeneca, Inc.), benzidine yellow (C.I. 21090 andC.I. 21100) and Hansa Yellow (C.I. 11680) as yellow colorants; organicdyes; and black materials such as carbon black, charcoal and other formsof finely divided carbon, iron oxide, zinc oxide, titanium dioxide, andthe like. Specific and preferred black colorants include Acid Black 48(Aldrich), Direct Black 58756 A (Crompton & Knowles), BPI MolecularCatalytic Gray (Brain Power), Fasday Cool Gray (Hunter Delator),Dispersol Navy XF Grains (Zeneca, Inc.), Dispersol Black CR-N Grains(Zeneca, Inc.), Dispersol Black XF Grains (Zeneca, Inc.), Disperse Black(BASF), Color Black FW18 (Degussa), Color Black FW200 (Degussa),Hostafine Black TS (Hoechst Celanese), Hostafine Black T (HoechstCelanese), Duasyn Direct Black (Hoechst Celanese), Pro-jet Black 1(Zeneca, Inc.) and Pro-jet Fast Black 2 (Zeneca, Inc.).

Printed Paper

The invention also features a printed, sized paper substrate producedusing the methods and compositions described herein. The printed, sizedpaper substrate of the invention can be produced by any of a variety ofprinting techniques, including inkjet printing, laserjet printing,photocopying, and the like. In general, the printing process involvesapplying an aqueous recording liquid to a sized paper substrate in animagewise pattern. Inkjet printing processes are well known in the art;see, for example, U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899;4,412,224; and 4,532,530.

The sized paper substrates of the invention can also be used in printingand/or copying process using dry or liquid electrophotographic-typedevelopers, such as electrophotographic processes, ionographic process,and the like. The sized paper substrates of the invention canadditionally be used in a process for generating images that involvesgenerating an electrostatic latent image on an imaging member in animaging apparatus, developing the latent image with a toner,transferring the developed image to a sized paper substrate of theinvention. Electrophotographic processes are known in the art; see,e.g., U.S. Pat. No. 2,297,691. Ionographic and electrographic processesare also well known in the art; see, e.g., U.S. Pat. Nos. 3,611,419;3,564,556; 4,240,084; 4,569,584; 2,919,171; 4,524,371; 4,619,515;4,463,363; 4,254,424; 4,538,163; 4,409,604; 4,408,214; 4,365,549;4,267,556; 4,160,257; and 4,155,093.

The sized paper substrate of the invention can also be used in any otherprinting or imaging processes, such as offset printing, printing withpen plotters, handwriting with ink pens, and the like.

EXPERIMENTAL

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toprepare and use the compounds disclosed and claimed herein. Efforts havebeen made to ensure accuracy with respect to numbers (e.g., amounts,temperature, etc.) but some errors and deviations should be accountedfor. Unless indicated otherwise, parts are parts by weight, temperatureis in EC and pressure is at or near atmospheric.

Also, in these examples, unless otherwise stated, the abbreviations andterms employed have their generally accepted meanings. Abbreviations andtradenames are as follows (note that suppliers of each material areindicated as well):

Amres=azetidinium polymer (Georgia Pacific);

Gum 280=starch (Penford);

Polectron=styrene/poly(vinyl pyrrolidone) copolymer (Polectron 430, ISPTechnologies);

PVOH=polyvinyl alcohol (Airvol 523S, Air Products);

PVP=polyvinyl pyrrolidone (Aldrich);

Sif=fumed silica (Aerosil MOX 170, Degussa);

Sip=precipitated silica (FK310, Degussa);

Tinopal=brightener (Ciba Additives);

Vantocil=3,12-diimino-2,4,11,13-tetraazatetradecanediimidamide, 20%aqueous solution (Vantocil IB, Zeneca, Inc.).

All patents, patent applications, journal articles and other referencesmentioned herein are incorporated by reference in their entireties.

Example 1 Polyazetidinium-based Size Press Coatings

The following table summarizes exemplary sizing compositions inaccordance with the invention, wherein the sizing agent is anazetidinium polymer. Each of the representative formulations waseffective to produce a sized substrate having the beneficial featuresdescribed herein, i.e., with respect to bleeding, wicking andwater-fastness.

Formulation Starch Azetidinium Binder Styrene/PVP Pigment Viscosity, No.(Gum 280) (“Amres”) (PVOH) (“Polectron”) 1:4 Sif:Sip % Solids cP pH 84-153 20 7.0 20.0 14.5 85-1 52.5 20 7.0 20.0 14.6 74-2 22 38 8.0 32.0 13.374-3 22 40 10.0 28.0 13.3 335 3.82 74-4 10 50 10.0 25.0 13.3 79-1 13 5011.0 26.0 16.3 3.75 71-2 22 36 9.4 32.8 25.3 3.74 76-1 22 38 6.0 2.032.0 13.3 348 3.73 76-2 22 36 6.0 4.0 32.0 13.3 74-1 22 33 8.0 5.0 32.013.3 479 3.86 76-3 22 34 6.0 6.0 32.0 13.3 286 3.73 77-3 22 35 5.0 6.032.0 13.3 77-2 22 34 5.0 7.0 32.0 13.3 250 3.73 72-2 22 33 5.0 8.0 32.023.1 3.74 78-2 22 33 5.0 8.0 32.0 14.1 667 4.0 77-4 22 38 10.0 10.0 20.013.1 3.79 79-2 35 10 10.0 10.0 35.0 18.8 4.10 77-1 27.5 47.5 12.5 12.510.8 3.75 78-1 22 33 5.0 8.0 32 15.4 182 6.70 90-1 23 30 10.0 35 14.590-2 23 30 10.0 35 14.7 90-3 23 30 10.0 35 13.4 90-4 23 30 10.0 35 14.5

Example 2 Polyguanidine-based Size Press Coatings

The following table summarizes exemplary sizing compositions inaccordance with the invention, wherein the sizing agent is apolyguanidine, an azetidinium polymer, or wherein the sizing agentcomprises a mixture of a polyguanidine and an azetidinium polymer. Eachof the representative formulations was effective to produce a sizedsubstrate having the beneficial features described herein, i.e., withrespect to bleeding, wicking and water-fastness.

Formulation Starch Azetidinium Polyguanidine Binder Styrene/PVP PigmentSolids No. (Gum 280) (“Amres”) (“Vantocil”) (PVOH) (“Polectron”) 1:4Sif:Sip (%) Tinopal pH 46-2 45 17 10 28.0 14.2 79-3 45 17 10 28.0 17.64.71 84-3 54 10 5 8 22.5 15.2 84-2 60 10 5 5 20.0 14.8 83-3 46 15 2 730.0 16.4 83-2 40 20 3 7 30.0 16.5 83-1 37 25 5 5 28.0 16.4 73-1 10 50 510 25.0 24.0 3.94 73-2 35 5 5 10 10 35.0 18.1 4.40 88-1 50 10 5 5 3014.5 6.61 88-2 50 10 5 5 30.0 14.5 6.62 89-3 25 10 10 5 5 40 16.2 5.089-2 38 12.4 4.8 9.5 4.8 28.6 14.3 1.90 88-3 55 10 5 5 23 14.0 2.0 89-140 13 5 10 30 13.8 2.0 51-5 60 40 12.5 52-1 50 50 13.3 55-2 71.4 14.36.0 55-3 85.5 17.1 5.4 51-4 25 25 50 20.0 53-4 90 10 6.0 53-1 73.7 26.34.8 53-2 54.5 22.7 22.7 5.5 54-4 71.4 14.3 14.3 6.6 57-1 71 14 14 6.6

What is claimed is:
 1. A paper product sized by the process comprisingapplying directly to an exposed surface of a paper substrate a singlesizing composition comprised of (a) a sizing agent selected from thegroup consisting of (i) an acidic salt of a guanidine polymer comprisedof monomer units having the structural formula (IV)

 wherein R³ is hydrogen or lower alkyl and R⁴ is hydrogen, alkyl,alkoxy, or hydroxyl-substituted alkoxy, and n is an integer in the rangeof 1 to 10 inclusive, (ii) a mixture of an azetidinium polymer and anacidic salt of a guanidine polymer comprised of monomer units having thestructural formula (IV) as described above, and (iii) a copolymer of anazetidinium monomer and a guanidine monomer, wherein the sizing agentrepresents approximately 5 wt. % to 95 wt. % of the sizing composition,based upon total solids weights of the sizing composition after drying;(b) optionally, up to 40 wt. % of a film-forming binder, wherein if thesizing agent is (i), or (iii), the film-forming binder is present; and(c) a liquid vehicle, wherein the sizing agent is admixed with theliquid vehicle prior to direct application of the sizing composition tothe substrate surface.
 2. The paper product of claim 1, wherein thesizing agent comprises an acidic salt of a guanidine polymer comprisedof monomer units having the structural formula (IV).
 3. The paperproduct of claim 1, wherein the sizing agent comprises a mixture of anazetidinium polymer and an acidic salt of a guanidine polymer comprisedof monomer units having the structural formula (IV).
 4. The paperproduct of claim 1, wherein the sizing agent comprises a copolymer of anazetidinum monomer and a guanidine monomer.
 5. The paper product ofclaim 2, wherein the guanidine polymer is a homopolymer.
 6. The paperproduct of claim 2, wherein the guanidine polymer is a copolymer.
 7. Thepaper product of claim 2, wherein R³ and R⁴ are hydrogen.
 8. The paperproduct of claim 3, wherein the azetidinium polymer is comprised ofmonomer units having the structural formula

in which: R¹ and R² are independently lower alkylene, X⁻ is an anionic,organic or inorganic counterion, and Y¹, Y² and Y³ are selected from thegroup consisting of hydrogen, hydroxyl, halo, alkoxy, alkyl, amino,carboxy, acetoxy, cyano and sulfhydryl.
 9. The paper product of claim 8,wherein: R¹ and R² are methylene, X⁻ is selected from the groupconsisting of halide, acetate, methane sulfonate, succinate, citrate,malonate, fumarate, oxalate and hydrogen sulfate, Y¹ and Y³ areindependently hydrogen or lower alkyl, and Y² is hydrogen or hydroxyl.10. The paper product of claim 9, wherein, in the azetidinium polymer,Y¹ and Y³ are hydrogen and Y² is hydroxyl.
 11. The paper product ofclaim 3, wherein R³ and R⁴ are hydrogen.
 12. The paper product of claim8, wherein R³ and R⁴ are hydrogen.
 13. The paper product of claim 9,wherein R³ and R⁴ are hydrogen.
 14. The paper product of claim 4,wherein the azetidinium monomer unit has the structural formula

in which: R¹ and R² are independently lower alkylene, X⁻ is an anionic,organic or inorganic counterion, and Y¹, Y² and Y³ are selected from thegroup consisting of hydrogen, hydroxyl, halo, alkoxy, alkyl, amino,carboxy, acetoxy, cyano and sulfhydryl, and the guanidine monomer unithas the structural formula

wherein n is an integer in the range of 1 to 10 inclusive, R³ ishydrogen or lower alkyl and R⁴ is hydrogen, alkyl, alkoxy, orhydroxyl-substituted alkoxy.
 15. The paper product of claim 14, wherein:R¹ and R² are methylene, X⁻ is selected from the group consisting ofhalide, acetate, methane sulfonate, succinate, citrate, malonate,fimarate, oxalate and hydrogen sulfate, Y¹ and Y³ are independentlyhydrogen or lower alkyl, and Y² is hydrogen or hydroxyl.
 16. The paperproduct of claim 1, wherein the liquid vehicle is aqueous.
 17. The paperproduct of claim 1, wherein the film-forming binder is present in thesizing composition.
 18. The paper product of claim 17, wherein thefilm-forming binder represents approximately 1 wt. % to 25 wt. % of thesizing composition composition, based upon total solids weight of thecomposition after drying.
 19. The paper product of claim 17, wherein thefilm-forming binder is selected from the group consisting ofpolysaccharides, polypeptides, synthetic vinyl polymers, cationicfilm-forming binders, and derivatives thereof.
 20. The paper product ofclaim 19, wherein the film-forming binder is a polysaccharide or aderivative thereof.
 21. The paper product of claim 19, wherein thepolysaccharide is starch.
 22. The paper product of claim 20, wherein thepolysaccharide is a cellulosic polymer.
 23. The paper product of claim20, wherein the polysaccharide is dextran.
 24. The paper product ofclaim 19, wherein the film-forming binder is a polypeptide.
 25. Thepaper product of claim 24, wherein the polypeptide is selected from thegroup consisting of collagen and gelatin.
 26. The paper product of claim17, wherein the film-forming binder is a synthetic vinyl polymer. 27.The paper product of claim 26, wherein the synthetic vinyl polymer isselected from the group consisting of poly(vinyl alcohol), poly(vinylphosphate), poly(vinyl pyrrolidone), vinyl-pyrrolidone-vinyl acetatecopolymers, vinyl alcohol-vinyl acetate copolymers, vinylpyrrolidone-styrene copolymers, and poly(vinylamine).
 28. The paperproduct of claim 27, wherein the synthetic vinyl polymer is a vinylpyrrolidone-styrene copolymer.
 29. The paper product of claim 27,wherein the film-forming binder is a cationic film-forming binder. 30.The paper product of claim 29, wherein the cationic film-forming binderis selected from the group consisting of quatemized vinylpyrrolidone-dimethylaminoethyl-methacrylate copolymer,dimethylaminoethyl-methacrylate-co-methyl methacrylate,polydiallyldimethyl ammonium chloride and quatermized aminoacrylatepolymers.
 31. A printed paper product prepared by a method, comprisingthe steps of: (A) applying to an exposed surface of a paper substrate asizing composition comprised of (1) a sizing agent selected from thegroup consisting of (a) an acidic salt of a guanidine polymer comprisedof monomer units having the structural formula (IV)

 wherein R³ is hydrogen or lower alkyl and R⁴ is hydrogen, alkyl,alkoxy, or hydroxyl-substituted alkoxy, and n is an integer in the rangeof 1 to 10 inclusive, (b) a mixture of an azetidinium polymer and anacidic salt of a guanidine polymer comprised of monomer units having thestructural formula (IV) as defined above, and (c) a copolymer of anazetidinium monomer and a guanidine monomer, (2) up to 40 wt. % of anoptional film-forming binder, and (3) a liquid vehicle, wherein thesizing agent is admixed with the liquid vehicle prior to directapplication of the sizing composition to the substrate surface, and (B)applying to the sized paper substrate a dye composition containing areactive dye having ionizable and/or nucleophilic groups capable ofreacting with the sizing agent thereby providing a sized substrate,wherein if the sizing agent is (a) or (c), then film-forming binder ispresent and the sizing agent represents approximately 5 wt. % to 95 wt.% of the sizing composition, based upon total solids weights of thesizing composition after drying.